Efficient multi-image bar code reader

ABSTRACT

An efficient multicamera imaging-based bar code reader for imaging a target bar code on a target object. An imaging system has a plurality of camera assemblies coupled to an image processing system. Each camera assembly includes a sensor array and an imaging lens assembly for focusing a field of view of the camera assembly onto a sensor array as well as including one or more light emitting diodes for illuminating a field of view of that camera assembly. One camera is activated or energized to detect an object and then all cameras are activated for generating images suitable to decode a bar code on the detected object.

FIELD OF THE INVENTION

The present invention relates to a multiple camera imaging-based barcode reader.

BACKGROUND OF THE INVENTION

Various electro-optical systems have been developed and used for readingoptical indicia, such as bar codes. A bar code is a coded pattern ofgraphical indicia comprised of a series of bars and spaces of varyingwidths, the bars and spaces having differing light reflectingcharacteristics. The pattern of the bars and spaces encode information.Bar code may be one dimensional (e.g., UPC bar code) or two dimensional(e.g., DataMatrix bar code). Systems that read, that is, image anddecode bar codes employing imaging camera systems are typically referredto as imaging-based bar code readers or bar code scanners.

Imaging-based bar code readers may be portable or stationary. A portablebar code reader is one that is adapted to be held in a user's hand andmoved with respect to a target indicia, such as a target bar code, to beread, that is, imaged and decoded. Stationary bar code readers aremounted in a fixed position, for example, relative to a point-of-salescounter. Target objects, e.g., a product package that includes a targetbar code, are moved or swiped past one of the one or more transparentwindows and thereby pass within a field of view of the stationary barcode readers. The bar code reader typically provides an audible and/orvisual signal to indicate the target bar code has been successfullyimaged and decoded. Sometimes barcodes are presented, as opposed toswiped. This typically happens when the swiped barcode failed to scan,so the operator tries a second time to scan it. Alternately,presentation is done by inexperience users, such as when the reader isinstalled in a self check out installation.

A typical example where a stationary imaging-based bar code reader wouldbe utilized includes a point of sale counter/cash register wherecustomers pay for their purchases. The reader is typically enclosed in ahousing that is installed in the counter and normally includes avertically oriented transparent window and/or a horizontally orientedtransparent window, either of which may be used for reading the targetbar code affixed to the target object, i.e., the product or productpackaging for the product having the target bar code imprinted oraffixed to it. The sales person (or customer in the case of self-servicecheck out) sequentially presents each target object's bar code either tothe vertically oriented window or the horizontally oriented window,whichever is more convenient given the specific size and shape of thetarget object and the position of the bar code on the target object.

A stationary imaging-based bar code reader that has a plurality ofimaging cameras can be referred to as a multi-camera imaging-basedscanner or bar code reader. In a multi-camera imaging reader, eachcamera system typically is positioned behind one of the plurality oftransparent windows such that it has a different field of view fromevery other camera system. While the fields of view may overlap to somedegree, the effective or total field of view of the reader is increasedby adding additional camera systems. Hence, the desirability ofmulticamera readers as compared to signal camera readers which have asmaller effective field of view and require presentation of a target barcode to the reader in a very limited orientation to obtain a successful,decodable image, that is, an image of the target bar code that isdecodable.

The camera systems of a multi-camera imaging reader may be positionedwithin the housing and with respect to the transparent windows such thatwhen a target object is presented to the housing for reading the targetbar code on the target object, the target object is imaged by theplurality of imaging camera systems, each camera providing a differentimage of the target object. U.S. patent application Ser. No. 11/862,568filed Sep. 27, 2007 entitled ‘Multiple Camera Imaging Based Bar CodeReader’ is assigned to the assignee of the present invention and isincorporated herein by reference.

SUMMARY OF THE INVENTION

The present disclosure concerns a multi-camera imaging-based bar codereader and a method of operating a multicamera imaging-based bar codereader in an efficient manner.

In some uses, a barcode reader that has multiple imagers or cameras in asingle housing can provide better functionality than a reader havingonly a single imager. Such readers have multiple illumination systems toilluminate the fields of view of multiple imagers or cameras. Forexample, a system that uses six imagers will have six illuminationsystems, one associated with each imager.

An illustrative multi-camera imaging-based bar code reader for imaging atarget bar code on a target object has a housing supporting one or moretransparent windows for viewing objects. An imaging system has a numberof cameras positioned within a housing interior region that define afield of view which is different than a field of view of each othercamera in the reader. Each camera includes a sensor array and its ownillumination system such as one or more light emitting diodes. An imageprocessing system includes a processor having a stored program forevaluating images from a subset of cameras that define the bar codereader field of view to determine a presence of a target object and oncea target object is detected, to activate an additional one or morecameras for use in decoding a barcode.

These and other objects, advantages, and features of the exemplaryembodiment of the invention are described in detail in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a bar code reader having a vertical anda horizontal window through which bar codes are viewed by multiplecameras within the reader;

FIG. 2 is a perspective view of the reader of FIG. 1 with a portion ofthe reader housing removed to illustrate a plurality of cameras;

FIGS. 3 and 4 are perspective views showing a position of threeadditional cameras on a printed circuit board resulting in a total ofsix cameras;

FIG. 5 is a schematic block diagram of selected systems and electricalcircuitry of the bar code reader of FIG. 1; and

FIG. 6 is a flowchart of an exemplary embodiment of the invention.

DETAILED DESCRIPTION

An exemplary embodiment of a multicamera imaging-based bar code scanneror reader 10 of the present invention is shown schematically in theFigures. As depicted in FIG. 7, the bar code reader 10 includescircuitry 11 comprising an image system 12 which includes a plurality ofimaging cameras C1, C2, C3, C4, C5, C6, which produce raw gray scaleimages, and an image processing system 14, which includes one or moreprocessors 15 and a decoder 16 that analyzes the gray scale images fromthe cameras and decodes imaged target bar codes, if present. The imagingsystem 12 is capable of reading, that is, imaging and decoding both 1Dand 2D bar codes and postal codes. The reader 10 is also capable ofcapturing images and signatures. The decoder 16 may be integrated intothe reader 10 or may be a separate system, as would be understood by oneof skill in the art.

In one exemplary embodiment, the reader 10 is stationary and the imageand decoder systems are supported within an interior region 18 of ahousing 20 (see FIG. 1). The housing 20 may be integrated into a salescounter that of a point of sales system that includes, for example, acash register, a touch screen visual display or other type userinterface and a printer for generating sales receipts. The housing 20depicted in FIG. 1 includes two transparent windows H, V.

In the exemplary embodiment, the cameras C1-C6 are mounted to a printedcircuit board 22 inside the housing and each camera defines a twodimensional field of view FV1, FV2, FV3, FV4, FV5, FV6. Positionedbehind and adjacent to the windows H, V are reflective mirrors M thathelp define a given camera field of view such that the respective fieldsof view FV1-FV6 pass from the housing 20 through the windows creating aneffective total field of view TFV for the reader 10 in a region of thewindows H, V, outside the housing 20. Because each camera C1-C6 has aneffective working range WR (shown schematically in FIG. 5) over which atarget bar code 30 may be successfully imaged and decoded, there is aneffective target area in front of the windows H, V within which a targetbar code 30 presented for reading may be successfully imaged anddecoded.

In the exemplary reader, three of the cameras C4-C6, look out of avertical window V with the help of reflecting mirrors and three camerasC1-C3 look out of a horizontal window H. In use, a user slides a packageor container 32 with a barcode through a region in front of the windows.The barcode may be visible to cameras behind the vertical window, or tocameras behind the horizontal window, or both. The barcode may movethrough the center of the field of view of the cameras, or through oneend or the other of the field of view.

Each camera assembly C1-C6 of the imaging system 12 captures a series ofimage frames of its respective field of view FV1-FV6. The series ofimage frames for each camera assembly C1-C6 is shown schematically asIF1, IF2, IF3, IF4, IF5, IF6 in FIG. 7. Each series of image framesIF1-IF6 comprises a sequence of individual image frames generated by therespective cameras C1-C6. As seen in the drawings, the designation IF1,for example, represents multiple successive images obtained from thecamera C1. As is conventional with imaging cameras, the image framesIF1-IF6 are in the form of respective digital signals representative ofraw gray scale values generated by each of the camera assembly C1-C6.

An exemplary illumination system 60 has one or more high energy lightemitting diodes L1-L6 associated with each of the cameras C1-C6. Thesehigh power LEDs when simultaneously energized generate sufficient heatto raise the internal temperature of the reader 10 to an undesirabledegree. Excessive heat can reduce the reliability and brightness of theLEDs, can reduce the signal quality of the image system and can alsoreduce the reliability of other electronic systems that are enclosed inthe housing interior 11 along with the imagers and illumination systems60. The housing of the reader must be sealed to keep dust and othercontaminants off the optical system so that the reader cannot be cooledwith vents or fans that circulate external air into the housing.

The image sensors themselves also use power and thus generate heat,adding to the bad effects heat buildup in the housing produce. Sinceheat cannot be easily expelled from the reader housing, it is one goalof the exemplary system to reduce heat generation within the housing.This is done without degrading the performance of the reader. Inparticular, bar code readers must be able to read barcodes that aremoving through the total field of view TFOV with a speed ofapproximately 100 inches per second, regardless of the orientation ofthe target object with respect to the windows and regardless on whatside of the object contains the bar code.

In accordance with one use, either a sales person or a customer willpresent a product or target object 32 selected for purchase to thehousing 20. More particularly, a target bar code 30 imprinted or affixedto the target object will be presented in a region near the windows H, Vfor reading, that is, imaging and decoding of the coded indicia of thetarget bar code. Upon a successful reading of the target bar code, avisual and/or audible signal will be generated by the reader 10 toindicate to the user that the target bar code 30 has been successfullyimaged and decoded. The successful read indication may be in the form ofillumination of a light emitting diode (LED) 34 a (FIG. 5) and/orgeneration of an audible sound by a speaker 34 b upon generation of anappropriate signal from the decoder 16.

In order to reduce heat generation and power consumption, theillumination LEDs and/or image sensors S1-S6 are de-energized wheneverthey are not needed to read barcodes. In order for the scannersperformance to not be negatively impacted, however, the components mustbe energized very quickly as soon as a barcode, or an object that mightbe bearing a barcode enters the scan field. This energization must bevery quick because the ability of the imagers to capture image frames islimited to around 30 or 60 frames per second, depending on what kind ofimage sensor is being used. A barcode can be traveling through the fieldso fast that the imager only has the opportunity to capture one or twoimages of the barcode before it passes out of the field. A delay inenergizing either the illumination system or an image sensor cantherefore reduce the probability that a good image (an image thatcontains a decodeable image of a barcode) will be captured.

In the preferred embodiment of this invention, one of the cameras, alongwith its associated illumination system is used to provide an earlydetection of an object entering the scan field. Once an object isdetected, the rest of the imagers and their illumination systems can beactivated. As the object moves through the scan field, the multipleimagers capture images in sequence, as described in co-pending patentapplication Ser. No. 11/862,568, until such time as a decodeable imagehas been captured and a decode accomplished, whereupon the illuminationsystems and/or some of the image sensors are immediately turned off andthe scanner returns to the starting condition where only one of thecameras is being used to detect an approaching object. It may also bebeneficial to use more then one camera to sense an object moving intothe field, to assure the full number of cameras is always enabled assoon as possible, but the essence of this invention is that a subset ofthe cameras is used to first detect an object and then all cameras areused to image it and decode the bar code affixed to it.

In a typical installation of this kind of scanner, it is known whichdirection a barcoded object will be moving as it enters the scan field.For example, in nearly all supermarkets, the scanner will be positionedin a check-stand such that objects move from the right to the left (+xdirection in FIG. 1) as seen when facing the vertical window of thescanner.

FIG. 1 illustrates a bar code reader with an operator moving an objectacross the scanner from the right to the left. A system of mirrorsdirects the field of view of two of the cameras upwards at around 45degrees through a horizontal window. Since the barcode will likely becoming into the field from the right, a camera C1 will be the first tobe able to detect the approaching object. This camera is thereforechosen as the one that is used to enable all the other cameras as soonas it has been determined that an object has entered its field of view.

In some situations different check-stand arrangements might result indifferent object transport directions, so the reader is adjusted by theuser to use different cameras as appropriate as an object identificationcamera. For example, a user might want the scanner to respond quickly toan object approaching from the left, so he/she can set-up the reader touse camera C3 which looks upwards to the left. It will also be possibleto set the scanner to use more then one camera if it isn't known whichway objects might be approaching. In either case, once a barcode hasbeen decoded, the scanner reverts to only using the specific imagersthat have been designated for object detection until an object isdetected. The camera that will be used for object detection can be setby scanning a special barcode or by sending appropriate instructionsthrough the interface from the host or by plugging in an auxiliary handheld scanner to a connector provided for that purpose and scanning abarcode. The scanner can also be shipped from the factory set as theuser desires, or at a factory determined default condition that is feltto be best for the majority of installations.

To make object detection even faster, the object detecting camera(s) cancapture partial frames in this object detection mode, as this allowsthem to capture data at a higher frame rate, so they can respond morequickly. The partial frames can be positioned towards the leading edgeof the field of view (the edge of the field of view where it is expectedthat the object will appear first). Once an object is detected, theimager reverts to full frame (or most of the frame if it has moreresolution then necessary) mode so it can read a barcode anywhere in theframe.

To avoid accidental detection of objects that are too far away to bereadable barcodes, the images collected when the camera is in sensing orobject detection mode can be examined for sharp transitions betweenlight and dark areas. Objects that are close enough to the scanner to bein the focus range of the imager optical system will have sharp edges,while those that are too far away to decode will be out of focus willhave slow transitions between light and dark areas. If the slope of thetransition between light and dark (or dark and light) is higher then athreshold, the scanner determines that the object is close enough topermit decoding a barcode on the object, and all of the imagers andtheir illumination systems are actuated until decode occurs. If decodedoesn't occur after a predetermined interval (user programmable) it isdecided that the scanner was falsely enabled and it returns to objectdetection mode. In some cases it should also be possible to program thescanner to make all the imagers remain activated for a few seconds aftera barcode is decoded. This will allow it to read more than one barcodein the field if the user moves more than one object into the field atone time.

The image processor or processors 15 controls operation of the camerasC1-C6. The cameras C1-C6, when operated during an imaging system,generate digital signals 35. The signals 35 are raw, digitized grayscale values which correspond to a series of generated image frames foreach camera. For example, for the camera C1, the signal 35 correspondsto digitized gray scale values corresponding to a series of image framesIF1. For the camera C2, the signal 35 corresponds to digitized grayscale values corresponding to a series of image frame IF2, and so on.The digital signals 35 are coupled to a bus interface 42, where thesignals are multiplexed by a multiplexer 43 and then communicated to amemory 44 in an organized fashion so that the processor knows whichimage representation belong to a given camera.

The image processors 15 access the image frames IF1-IF6 from memory 44and search for image frames that include an imaged target bar code 30′.If the imaged target bar code 30′ is present and decodable in one ormore image frames, the decoder 16 attempts to decode the imaged targetbar code 30′ using one or more of the image frames having the imagedtarget bar code 30′ or a portion thereof.

For any individual presentation of a target bar code 30 to the readerwindows H, V the exact orientation and manner of presentation of thetarget bar code 30 to the windows will determine which camera or camerasgenerate suitable images for decoding. As stated above, it is likelythat, for example, sales persons generally or a given sales person,specifically, will develop a pattern of presentation of a target barcode 30 to the windows H, V that results in certain cameras having ahigher probability of generating an image frame that includes the imagedtarget bar code 30′ and is suitable for decoding the imaged bar code30′, either alone or in conjunction with other image frames.

Each camera includes a charged coupled device (CCD), a complementarymetal oxide semiconductor (CMOS), or other imaging pixel array,operating under the control of the imaging processing system 40. In oneexemplary embodiment, the sensor array comprises a two dimensional (2D)CMOS array with a typical size of the pixel array being on the order of752×480 pixels. The illumination-receiving pixels of the sensor arraydefine a sensor array surface secured to a printed circuit board forstability. The sensor array surface is substantially perpendicular to anoptical axis of the imaging lens assembly, that is, a z axis that isperpendicular to the sensor array surface would be substantiallyparallel to the optical axis of the focusing lens. The pixels of thesensor array surface are disposed in an orthogonal arrangement of rowsand columns of pixels.

The reader circuitry 11 includes imaging system 12, the memory 44 and apower supply 11 a. The power supply 11 a is electrically coupled to andprovides power to the circuitry 11 of the reader. Optionally, the reader10 may include an illumination system 60 (shown schematically in FIG. 7)which provides illumination to illuminate the effective total field ofview to facilitate obtaining an image 30′ of a target bar code 30 thathas sufficient resolution and clarity for decoding.

The energy savings aspects of the exemplary reader are explained inrelation to the flowchart 110 of FIG. 6. For a subset of cameras(typically one such as the camera C3) an associated sensor array andlight emitting diode is enabled or activated 120 during an objectdetection period and images (possibly of lower resolution that used indecoding) of the field of view of the camera or cameras of the subsetare captured 122. The processor 15 associated with the camera thendetermines 124 if a target is within the field of view of the particularcamera say camera C1, by evaluating each image frame of the series ofimage frames IF1. If the processor determines an object is present in animage, the processor then (optionally) determines 126 if the object iswithin the working range of the reader.

If an object is detected the processor 15 activates 130 all the cameraassemblies C1-C6 which begin to capture 132 series of image framesIF1-IF6 from all six cameras. Since many of these captured framesIF1-IF6 will not include an imaged target bar code 30′, the imageprocessors 15 of the image processing system 14 analyze the stored imageframes IF1-IF6 in memory 44 to find and decode the bar code.

The one or more processors check images 134 to determine if a successfulread has occurred. A successful image decode causes the processor orprocessors to process that in a variety of ways such as provide asignal, transmit the bar code data and set up criteria for use by theprocessors in determining 140 whether to suspend decode leads to adecision step 140 where the processors determine whether to suspendimaging operation of all six cameras and put the reader back into objectdetection mode or try to decode more barcodes. This is based on theknowledge that a successful decode may be followed by a user swiping anumber of objects in succession and therefore the need to power down anumber of cameras is decreased.

For each camera assembly C1-C6, electrical signals are generated byreading out of some or all of the pixels of the pixel array after anexposure period generating the gray scale value digital signal 35. Thisoccurs as follows: within each camera, the light receivingphotosensor/pixels of the sensor array are charged during an exposureperiod. Upon reading out of the pixels of the sensor array, an analogvoltage signal is generated whose magnitude corresponds to the charge ofeach pixel read out. The image signals 35 of each camera assembly C1-C6represents a sequence of photosensor voltage values, the magnitude ofeach value representing an intensity of the reflected light received bya photosensor/pixel during an exposure period.

Processing circuitry of the camera assembly, including gain anddigitizing circuitry, then digitizes and coverts the analog signal intoa digital signal whose magnitude corresponds to raw gray scale values ofthe pixels. The series of gray scale values GSV represent successiveimage frames generated by the camera assembly. The digitized signal 35comprises a sequence of digital gray scale values typically ranging from0-255 (for an eight bit A/D converter, i.e., 2⁸=256), where a 0 grayscale value would represent an absence of any reflected light receivedby a pixel during an exposure or integration period (characterized aslow pixel brightness) and a 255 gray scale value would represent a veryintense level of reflected light received by a pixel during an exposureperiod (characterized as high pixel brightness). In some sensors,particularly CMOS sensors, all pixels of the pixel array are not exposedat the same time, thus, reading out of some pixels may coincide in timewith an exposure period for some other pixels.

As is best seen in FIG. 5, the digital signals 35 are received by thebus interface 42 of the image processing system 40, which may includethe multiplexer 43, operating under the control of an ASIC 46, toserialize the image data contained in the digital signals 35. Thedigitized gray scale values of the digitized signal 35 are stored in thememory 44. The digital values GSV constitute a digitized gray scaleversion of the series of image frames IF1-IF6, which for each cameraassembly C1-C6 and for each image frame is representative of the imageprojected by the imaging lens assembly onto the pixel array during anexposure period. If the field of view of the imaging lens assemblyincludes the target bar code 30, then a digital gray scale value image30′ of the target bar code 30 would be present in the digitized imageframe.

The decoding circuitry 14 then operates on selected image frames andattempts to decode any decodable image within the image frames, e.g.,the imaged target bar code 30′. If the decoding is successful, decodeddata 56, representative of the data/information coded in the target barcode 30 is then output via a data port 58 to an external computer whichalso may communicate data to the reader used in reprogramming the cameraused to detect objects. A successful decode can also be displayed to auser of the reader 10 via a display output 59. Upon achieving a goodread of the target bar code 30, that is, the bar code 30 wassuccessfully imaged and decoded, the speaker 34 b and/or an indicatorLED 34 a is activated by the bar code reader circuitry 11 to indicate tothe user that the target bar code 30 has successfully read.

While the present invention has been described with a degree ofparticularity, it is the intent that the invention includes allmodifications and alterations from the disclosed design falling withinthe spirit or scope of the appended claims.

I claim:
 1. A multi-camera imaging-based bar code reader for imaging atarget bar code on a target object, the bar code reader comprising: ahousing supporting one or more transparent windows and defining aninterior region, a target object being presented in relation to thehousing for imaging a target bar code; an imaging system including aplurality of cameras wherein each camera is positioned within thehousing interior region and defines a field of view which is differentthan a field of view of each other camera of the plurality of camerasand combine to form a bar code reader field of view, each cameraincluding a sensor array; and an image processing system comprising aprocessor having a stored program for evaluating images from a subset ofcameras that define the bar code reader field of view to determine apresence of a target object and once a target object is detected, toactivate an additional one or more cameras for use in decoding abarcode.
 2. The bar code reader of claim 1 wherein the processing systemdetermines an optimum subset of cameras for determining a presence of atarget object based on a user input.
 3. The bar code reader of claim 1wherein in determining a presence of a target object based on imagesfrom the subset of cameras the image processing system evaluates partialimages.
 4. The bar code reader of claim 1 wherein the image processingsystem determines if the object is within a working range of the reader.5. A method of operating a multi-camera imaging-based bar code readerfor imaging a target bar code comprising: providing an imaging-based barcode reader including a housing supporting one or more transparentwindows and defining an interior region; positioning multiple camerashaving sensor arrays within the housing interior to define differentfields of view for each of said plurality of cameras to define a barcode reader field of view; activating a subset of cameras less than atotality of cameras in said reader to detect an object moving through oroccupying a position within a field of view of one or more cameras insaid subset of cameras; activating additional cameras not in said subsetand obtaining images from said additional cameras to decode a bar codeon said target object; and interpreting images from the multiple camerasto decode a bar code on the target object.
 6. The method of claim 5wherein before activating the additional cameras, a processor determinesif the object that was sensed is moving or located within a workingrange of the reader.
 7. The method of claim 5 wherein the subset is asingle camera and wherein the single camera is chosen based on typicaluser tendencies in scanning objects through the reader's field of view.8. The method of claim 5 wherein the step of activating additionalcameras includes turning on an LED associated with the additionalcameras as well as activating sensor arrays of said additional cameras.9. The method of claim 5 additionally comprising adjusting the subset ofcameras based on varying parameters.
 10. The method of claim 5additionally comprising evaluating the position of the object beforeactivating the additional cameras.
 11. The method of claim 10 whereinthe step of evaluating a position of the object is performed byevaluating transitions from dark to light in the image.
 12. The methodof claim 5 wherein the object detection is performed on partial imageframes from the subset of cameras to speed object detection.
 13. Themethod of claim 12 wherein a leading edge of an image is used indetecting the object.
 14. An imaging system for use in a multi-cameraimaging-based bar code reader having a housing supporting one or moretransparent windows and defining an interior region, a target objectbeing presented to the plurality of windows for imaging a target barcode on a target object, the imaging system comprising: a plurality ofcamera assemblies coupled to an image processing system, each cameraassembly of the plurality of camera assemblies being positioned withinthe housing interior position and defining a field of view which isdifferent than a field of view of each other camera assembly of theplurality of camera assemblies, each camera assembly including a sensorarray, an imaging lens assembly for focusing the field of view of thecamera assembly onto the sensor array and an illumination device thathelps define a camera field of view; and one or more processors forevaluating images captured by one camera assembly to first determine apresence of an object within a reader field of view and then to searchfor decodable bar code on an object from images from other cameraassemblies of said plurality of camera assemblies.
 15. The imagingsystem of claim 14 wherein the one or more processors activate sensorarrays and illuminating devices for certain camera assemblies only afteran object is detected in a reader field of view.
 16. The imaging systemof claim 14 including a communications port for communicating with otherdevices for reprogramming an object search routine of said one or moreprocessors.
 17. The imaging system of claim 14 wherein the one or moreprocessors evaluate lower resolution images from the one camera assemblyin determining a presence of an object in the reader field of view. 18.A multi-camera imaging-based bar code reader for imaging a target barcode on a target object, the bar code reader comprising: housing meanssupporting a plurality of transparent windows and defining an interiorregion bounded in part by the plurality of windows for imaging a targetbar code; imaging means including a plurality of camera assemblies meanscoupled to an image processing system means wherein each camera assemblymeans of the plurality of camera assemblies means is positioned withinthe housing interior and define a field of view which is different thana field of view of each other camera assembly means of the plurality ofcamera assemblies means; sensing means for each camera assembly meansincluding a sensor array, an imaging lens assembly for focusing thefield of view of the camera assembly means onto the sensor array, and anilluminating device for shining light onto a camera assembly field ofview; memory means for storing images from the sensing means; processingmeans for determining a presence of an object by activating one cameraassembly, evaluating images from the one camera assembly and activatingadditional camera assemblies once an object is detected; and decodermeans for evaluating images from a plurality of camera assemblies fordetermining a content of an identified bar code on a detected object.19. Computer-readable media having computer-executable instructions forperforming a method of operating an imaging-based bar code reader havingmultiple cameras for efficiently imaging a target bar code on a targetobject, the steps of the method comprising: activating a subset ofcameras less than a totality of cameras in said reader to detect atarget object moving through or occupying a position within a field ofview of one or more cameras in said subset of cameras; activatingadditional cameras not in said subset and obtaining images from saidadditional cameras and storing said images in a memory; and interpretingimages from the multiple cameras in the bar code reader to decode a barcode on the target object.
 20. The computer readable medium of claim 19wherein before activating the additional cameras the instructionsdetermine if the object that was sensed is moving or located within aworking range of the reader.
 21. The computer readable medium of claim19 wherein the subset is a single camera and wherein the instructionschoose said single camera based on typical user tendencies in scanningobjects through the reader's field of view.
 22. The computer readablemedium of claim 19 wherein the instructions activate additional camerasincluding turning on an LED associated with the additional cameras aswell as activating sensor arrays of said additional cameras.
 23. Thecomputer readable medium of claim 19 wherein the instructions adjust thesubset of cameras based on varying parameters.